1. Field of the Invention
This invention relates to subsea flowline connection systems and more particularly to a remote controlled system for precise alignment and connection of bundles of flowlines.
2. Description of the Prior Art
The production of oil and gas from offshore wells has developed into a major endeavor of the petroleum industry. Wells are commonly drilled several hundred or even several thousand feet below the surface of the ocean. These wells must not only be drilled without the use of divers at the deeper depths, but the connecting, testing and servicing of pipes and of regulating valves must be performed on these wells during and after the drilling process.
One of the major problems of subsea installation is the connecting of flowlines to transport the oil from the well after the well has been drilled and a subsea Christmas tree assembly has been lowered and fastened in place on the well. A plurality of short flowline loops are connected to the Christmas tree assembly before the tree assembly is lowered into place atop the well, with the free ends of the flowline loops gathered together and supported above the seafloor to facilitate connecting other flowline to the treeside flowline loops. Another plurality of flowlines has the first ends thereof connected to a storage container and the second ends thereof gathered into a bundle and lowered to the seafloor for connection to the flowline loops on the tree assembly. The flowline bundle is then pulled across the seafloor into alignment with the flowline loops so that the flowline bundle and the flowline loops can be connected together in a fluid-tight connection.
Some of the prior art flowline connecting facilities include a collar or flange connected around the flowline bundle and a pull-in cable attached to the flange at one side of the bundle. This collar and cable arrangement causes the ends of the flowlines to be pointed away from the axis of the ends of the flowline loops as the flowlines are moved toward the flowline loops. The flowlines on the side of the flowline bundle nearest the cable move slightly ahead of the other flowlines as the bundle is pulled across the seafloor. This results in uneven pressure around the seals when the flowlines and the flowline loops join and may cause these seals to fail. The axial orientation of the flowlines caused by collar and cable arrangement also increase the forces required to rotationally orient the flowlines and the flowline loops. Some of these problems would be reduced or eliminated if the cable were attached to the geometric center of the flowline bundle.
To solve the critical problem of obtaining exact alignment while the sealing members are being engaged, some of the prior art flowline connecting facilities use several "stages of alignment" with each of the subsequent stages of alignment absorbing and overcoming all of the forces needed to effect the previous stage of alignment plus the additional force needed to effect a more precise stage of alignment. As a result the components for each stage of alignment must be large enough to handle these large forces. Also the accumulation of all of the forces, including the forces needed to drag the flowline bundle into position initially are still present when the final precision sealing members are engaged.
What is needed is an apparatus which can pull the flowline bundle into a position adjacent the flowline loop and can provide the forces needed to hold the flowline bundle in place while another portion of the apparatus supplies a smaller force to precisely align the flowline loop with the flowline bundle and move the flowline loop into fluid-tight connection with the flowline bundle.